Anthropogenic Climate Change

In 2008, climate scientists celebrated the 50th anniversary of the Keeling Curve, one of the iconic images of science, rivaling the double helix or Darwin's sketches of finches. March 1958 marked the inception of the historical recording of atmospheric carbon dioxide levels at a small observatory on top of Hawaii's Mauna Loa. As the measurements progressed over the years, Dr. Keeling noted a steady increase of about 1.5 ppm (parts per million) per year (Figure 1). His plot provides clear evidence that carbon dioxide accumulates in the atmosphere as the result of mankind's use of fossil fuels, turning speculations about increasing CO2 from a hypothesis into a fact.

The World Meteorological Organization and the United Nations Environment Program established the Intergovernmental Panel on Climate Change (IPCC) in 1988, assigning it to assess the scientific, technical, and socioeconomic information relevant to human-induced climate change and its potential risks. The IPCC does not support research directly or monitor climate-related data, but its assessment reports have often inspired scientific research in many climate-oriented fields, leading to new findings. The IPCC has published a total of four assessment reports, becoming the de facto accurate and relevant standard regarding scientific facts on global climate change and its impacts.

The IPCC has three Working Groups and one Task Force:

The WGI for the First Assessment Report (FAR) was completed in May 1990. Its nonquantitative findings for an anthropogenic interference [Page 83]with the climate system remain valid today. It correctly concluded that “emissions resulting from human activities are substantially increasing the atmospheric concentrations of the greenhouse gases: CO2, CH4, CFCs, N2O.” The FAR introduced varying levels of confidence, ranging from “certainty” to expert “judgment” (Table 1).

Figure 1 The Keeling Curve from 1958 to 2009

Source: Data from Scripps CO2 Program. Retrieved December 10, 2009, from http://scrippsco2.ucsd.edu/graphics_gallery/mauna_loa_record/mauna_loa_record.html. Last updated January 2009.

Notes: Monthly average atmospheric carbon dioxide concentration versus time at Mauna Loa Observatory, Hawaii (20° N, 156° W), where CO2 concentration is in parts per million (ppm) in the mole fraction. The curve is a fit to the data based on a stiff spline plus a 4-harmonic fit to the seasonal cycle with a linear gain factor.

The Second Assessment Report (SAR) was released in November 1995. The report reaffirmed that “the balance of evidence suggests a discernible human influence on global climate.” SAR provided key input to the negotiations that led to the adoption in 1997 of the Kyoto Protocol.

The Third Assessment Report (TAR) was approved at the government plenary in January 2001. The main conclusion from TAR strengthened the finding from SAR: “The Earth's climate system has demonstrably changed on both global and regional scales since the preindustrial era, with some of these changes attributable to human activities.”

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